1. Field of the Invention
The present invention relates to the purification of saline solutions and, more particularly, to an improved process for selectively extracting salts from aqueous media such as sea water, industrial streams, ground waters and the like.
2. Brief Description of the Prior Art
As known, prior artisans have throughout history considered saline waters, such as the vast oceans, as a potential or source for the ever-increasing demand for fresh water. In recent years, the actual necessity for recovering demineralized water from salt containing aqueous media, such as sea water or certain industrial streams, has become increasingly significant both from a standpoint of obtaining fresh water for human consumption and/or providing purified waters for ecology purposes.
To a large extent, the somewhat extensive research efforts in this area have been directed to three basic desalination processes. These are: distillation, electrodialysis and freezing. Distillation techniques typically involve multistage or effect procedures wherein preheated sea water is introduced into a series of stages with the water being flashed into steam or vapor and utimately recovered as pure water. In electrodialysis, a large chamber is divided into compartments by thin sheets called membranes. Two alternately positioned types of membranes are employed. One allows positive ions to pass while the other lets only negative ions through. When an electric current is sent through the water, the negative ions are drawn through the membranes permeable to the negative ions toward the positive electrode. Likewise, the positive ions are drawn through the membrane permeable to positive ions toward the negative electrodes. Freezing techniques are based on the fact that when sea or salt water freezes, the ice crystals that are produced are pure water in solid form. Thus, the salt that is separated and trapped between the ice crystals, may be removed by washing with fresh water with the ice then being melted to obtain free water. A further and perhaps more recent technique involves liquid extraction wherein solvents capable of "extracting" the water and rejecting the salts, are used in otherwise conventional liquid-liquid extraction procedures. Specific examples of such solvents include 2-ethylhexylamine, methyl benzyl amine and phenyl ethanol amine.
While the above procedures are known and have achieved, at least to some extent, commercial significance, in general they suffer from certain disadvantages and/or difficulties. For example, they often require large amounts of energy as well as large capital expenditures. Further, such known techniques are sometimes very complex and require elaborate processing operations. Known extraction processes are also often complex and generally less than effective since the extracted water must, in turn, be recovered from the solvent. The present invention is directed to an advanced in the art relative to the removal of salts from aqueous saline solutions.